# Question ebe44

Jan 14, 2018

Here's why.

#### Explanation:

The idea here is that the calcium cation, ${\text{Ca}}^{2 +}$, carries a $2 +$ charge and the hypochlorite anion, ${\text{ClO}}^{-}$, carries a $1 -$ charge, so in order for the two ions to form an ionic compound, they must combine in a $1 : 2$ ratio.

Since ionic compounds are neutral, the overall negative charge coming from the anions must balance out the overall positiev charge coming from the cations.

In this case, you will need $2$ hypochloriet anions to get a total negative charge of

$2 \times \left(- 1\right) = 2 -$

in order to balance out the $2 +$ charge of the calcium cation.

To show that we need $2$ hypochlorite anions for every $1$ calcium cation, we use parentheses around the hypochlorite anion and a subscript of $2$.

"Ca"("ClO")_ 2 => "1 formula unit of Ca"("ClO") = {(1 xx "Ca"^(2+)), (2 xx "ClO"^(-)) :}#

The parentheses are used to show that the subscript is applied to both elements that make up the anion, i.e. to $\text{Cl}$ and $\text{O}$.

By comparison, something like

${\text{CaClO}}_{2}$

would imply that the subscript is only applied to the oxygen atoms, which would be incorrect given the fact that the hypochlorite anion contains $\text{Cl}$ and $\text{O}$.